1. Field of the Invention
This invention relates to polycarbonates and more particularly to flame retardant polycarbonates having a perfluoroalkane sulfonate salt incorporated therein along with a halogenated aromatic anhydride.
2. Description of the Prior Art
Polycarbonates derived from reactions involving organic dihydroxy compounds and carbonic acid derivatives have found extensive commercial application because of their excellent mechanical and physical properties. These thermoplastic polymers are particularly suited for the manufacture of molded products requiring impact strength, rigidity, toughness, thermal and dimensional stability as well as excellent electrical properties.
In certain end use applications, the polycarbonate article is required to meet certain flammability requirements. In order to achieve a particular flame retardancy requirement, additives are well known which reduce or extinguish the flame spread of a normally flammable or fire retardant polycarbonate resin. Even though flame spread may be eliminated, when the polycarbonate is contacted with flame, the heat causes it to drip and the molten and sometimes flaming polymer may drip onto flammable materials and ignite them.
It has been recognized that perfluoroalkane sulfonates impart improved flame resistance to polycarbonates in which they are incorporated. Exemplary of this recognition is U.S. Pat. No. 3,775,367.
Although these perfluorinated alkali metal or ammonium sulfonates provide improved flame retardancy, they do not necessarily provide sufficient drip suppression.
In accordance with the present invention a polycarbonate is provided which imparts flame retardancy or self-extinguishing characteristics and suppressed dripping during flaming.